Ivan Velazquez Caballero, said to be the drug cartel's No. 3 leader, had engaged in a violent split from the group. His arrest is likely to weaken his faction, if not the Zetas as a whole.

MEXICO CITY — Mexican authorities working closely with their U.S. counterparts scored big in the fight against drug cartels with the capture of a top leader of Mexico's most vicious criminal gang, the Zetas paramilitary force.

Ivan Velazquez Caballero, who used aliases that included "Zeta-50" and "El Taliban," was presented to reporters Thursday in Mexico City by masked naval special forces.

Navy spokesman Vice Adm. Jose Luis Vergara said Velazquez was captured a day earlier when the marines surrounded one of his residences in the eastern city of San Luis Potosi. He was seized with two accomplices and minimal resistance, Vergara said.

Velazquez commanded a faction of the Zetas that had recently engaged in a bloody split with the rest of the organization, according to officials and experts. Fighting between the two groups has been linked to a spate of killings, dumped bodies and other mayhem in an important and once-calm central swath of the country, from San Luis Potosi to Zacatecas.

Military sources say he was partly responsible for expanding the Zetas operations deep into that region, working since 2007 and today leading 400 gunmen.

His capture follows other high-profile arrests this month of top leaders of the rival Gulf cartel, as President Felipe Calderon presses in the final weeks of his government to cement a legacy based in large part on dismantling powerful drug-trafficking networks.

By the government's count, 13 of 24 fugitive cartel leaders put on a bounty list in 2009 have been captured or killed. Yet bloodshed, kidnapping and other forms of violent organized crime have spread to more parts of the country. More than 55,000 people have been killed since Calderon launched the offensive nearly six years ago.

Velazquez, considered to be No. 3 in the Zeta leadership, had fought with its No. 2, a particularly brutal capo, Miguel Angel Trevino Morales, aka "Z-40," and with Heriberto Lazcano, historical leader of the group. Velazquez and Trevino were apparently locked in a showdown over control of San Luis Potosi, the military said, where 14 mutilated bodies were found last month piled inside a truck.

Banners purportedly signed by Velazquez also appeared in the city, accusing Trevino and his followers of being traitors. A few days later, Trevino sent bulldozers to destroy one of Velazquez's homes in the Zacatecas city of Fresnillo, according to residents.

Atty. Gen. Marisela Morales, in describing the internal Zetas struggle, suggested that Velazquez may have sensed weakness or an opening at the top and chose to move on his erstwhile brothers-in-arms.

"All of this forms part of the fight to control territory and has always been a factor in rising violence," she said.

The government had offered a reward of slightly more than $2 million for Velazquez's detention, which Vergara said came as the culmination of a nine-month intelligence-gathering operation.

Though Velazquez's removal is a blow to his faction, it will not necessarily weaken the Zetas. It may allow Trevino and Lazcano — who have also had to battle challenges from the vast Sinaloa cartel — to consolidate their operations, smuggling routes and territory, minus one threat. It could usher in a lower level of violence, at least temporarily.

Where the capture could be especially valuable, like that of other cartel chieftains, is in the potential for more information that can be gleaned through interrogation. Velazquez would undoubtedly have detailed outlines of the Zetas' business in northeast and central Mexico, and would know who in the government and security forces are on the cartel payroll.

"[The] problem with arresting criminal leaders is there are 10 waiting to take his place," said a former U.S. military official familiar with Mexico's drug war, who spoke on condition of anonymity. "If they can't get enough information from him to take down the network, it will just drag things out."

In large part thanks to U.S. cooperation and technical training, Mexico has seen a steady, evolving improvement of the gathering and sharing of intelligence, and the willingness to act on it, especially by the marines. U.S. officers work particularly closely with the naval special forces, whom they regard as more flexible and receptive than the more stodgy army.

The U.S. has encouraged the targeting of the Zetas, notably in the area of Velazquez's operations, since the fatal shooting of an American federal officer on the road to San Luis Potosi in early 2011.

At the same time, Velazquez might have been betrayed by other Zetas who wanted to get rid of him, a frequent occurrence when cartels begin to fracture and become riven by infighting.

Velazquez was identified by authorities as the Zetas regional chief since 2007 of Zacatecas, Aguascalientes and parts of Guanajuato and Coahuila, the well-populated center of Mexico. The Zetas' gradual takeover of the central region has gone largely unreported by the Mexican press, further evidence of the cartels' ability to silence journalists and officials through intimidation or bribery.

Vergara said Velazquez also was in charge of Zetas operations in Monterrey, Mexico's wealthiest city, and handled money-laundering for the group.